1. Field of the Invention
The present invention relates to a light-emitting device using nano size needles, and more particularly, to a light-emitting device that improves injection efficiency of electrons or holes by providing electrons or holes to an emitting layer using nano size needles.
2. Description of the Related Art
Inorganic electroluminescence (EL) devices and organic EL devices have been developed as alternatives to displays such as cathode ray tubes (CRTs) or liquid crystal displays (LCDs). The inorganic EL devices are classified into alternating current types and direct current types. The alternating current inorganic EL device is a light-emitting device in which electrons accelerated by a high voltage collide with transition metal ions in a fluorescent substance dispersed in an organic binder such as a semiconductor, to emit light. A direct current inorganic EL device is a light-emitting device in which an electron and a hole are recombined in a p-n configuration of an inorganic semiconductor to emit light. On the other hand, the organic EL device is a light-emitting device in which electrons and holes are injected into organic materials from electrodes and the electrons and the holes are recombined in the organic matter to emit light. Organic EL devices can be widely utilized due to advantages such as response speeds as fast as those of CRTs, high brightness, low power consumption, wide viewing angle, and super thin film.
FIG. 1 schematically illustrates a conventional configuration of an organic EL device. Referring to FIG. 1, an organic EL device 100 includes an emitting layer 130 interposed between an anode 150 and a cathode 110, a hole transporting layer (HTL) 140 interposed between the anode 150 and the emitting layer 130 in order to improve injection efficiency of holes, and an electron transporting layer (ETL) 120 interposed between the cathode 110 and the emitting layer 130 in order to improve injection efficiency of electrons. In this configuration, the operation of the organic EL device is classified into (1) the operation of injecting electrons and holes into the emitting layer, (2) the operation of radiative recombination of electrons and holes, and (3) the operation of transmitting light to the outside.
The injection efficiency of electrons and holes need to be improved in order to improve the luminous efficiency of an organic EL device. Conventional techniques to improve the injection efficiency of electrons and holes include treating the surface of an electrode, or interposing an intermediate layer such as an electron injection layer, an electron transporting layer, or a blocking layer, between an electrode and an emitting layer. For example, in order to provide holes from an anode to an emitting layer, the work function of the anode must be high enough, and in order to provide electrons from a cathode to an emitting layer, the work function of the cathode must be low enough. Since materials that are stable and satisfy the requirement as describe above are difficult to obtain, a work function of an electrode is often increased or lowered using proper surface treatment. However, there is a limit to the increase or decrease of a work function using surface treatments, and the manufacturing process can be complicated. Accordingly, a new method is required to improve to injection efficiency of electrons and holes from electrodes to an emitting layer.